In the oil and gas industry, reservoir modeling involves constructing a computer model of a petroleum reservoir in order to improve estimation of reserves and making decisions regarding the development of the field. For example, geological models can be created to provide a static description of a reservoir prior to production. Reservoir simulation models may be created to simulate and predict the flow of fluids within a reservoir over its production lifetime.
One issue with reservoir simulation models is the challenge of modeling fractures within a reservoir, which requires a thorough understanding of matrix flow characteristics, fracture network connectivity and fracture-matrix interaction. Fractures can be open cracks or voids within the formation, and they can either be naturally occurring or artificially generated from a wellbore. Accurate modeling of fractures is important as fracture properties such as spatial distribution, aperture, length, height, conductivity, and connectivity significantly affect the flow of reservoir fluids to the well bore.
Mesh generation techniques are used in reservoir modeling. Two traditional mesh generation techniques for three-dimensional (3D) reservoir simulation are structured-based meshing and extrusion based meshing. In structured techniques, hexahedra are connected in a logical 3D i-j-k space with each interior mesh node being adjacent to 8 hexahedra. Extensions to structured techniques include local grid refinement where local regions of an original grid are replaced with finer grids. This can become time-consuming, computationally expensive, and prohibitively burdensome when dealing with general reservoir geometries, such as arbitrary 3D fracture surfaces. Because of the inherent 2.5 dimensional (2.5D) nature of existing extrusion techniques, similar limitations apply to these techniques. Alternative, fully unstructured meshing techniques exist, including tetrahedralization and polyhedral meshing schemes. The increased complexity of these techniques often leads to lower robustness as compared to structured techniques, especially, in the presence of imperfect geometry input (i.e., ‘dirty geometry’).